As an example of conventional resistor, Japanese Patent Laid-open Publication H3-80501 discloses “a resistor having a 4-layer side electrode.” The resistor comprises, as shown in FIG. 8, a resistor layer 13 connected to a pair of upper electrode layers 12 disposed at both of upper end portions of a substrate 11 and a pair of C-shaped side electrodes 14 disposed at both sides of the substrate 11 and electrically connected to the upper electrode layers 12. In the following description, the word “connection” means electrical connection.
The side electrode 14 has a laminated structure that comprises a C-shaped first metal thin film 15, formed of Ni—Cr thin film, Ti thin film or Cr thin film, which is the lowest layer connected to the upper electrode layer 12; a second metal thin film 16 formed of low resistance Cu thin film superposed on the first metal thin film 15; a first metal-plated layer 17 formed of Ni plated layer superposed on the second metal thin film 16; and further a second metal-plated layer 18 formed of Pb—Sn plated layer or Sn plated layer superposed on the first metal-plated layer 17.
In the case of a resistor disclosed in Japanese Patent Laid-open Publication H3-80501, since the upper electrode 12 and resistor layer 13 are fabricated by a thick film technology, and the second metal thin film 16 of the side electrode is formed of low resistance Cu thin film, there arises a problem such that the connection resistance is high between the upper electrode 12 and the resistor layer 13 and, in addition, the second metal thin film 16 is liable to peel off from the first metal thin film 1. That is, if the resistor is kept in a high humidity atmosphere, the Cu thin film 16 will be easier to peel off from the first metal thin film 15. The cause of this peel-off is thought that as there exists no solid solution between the Cu thin film 16 and the first metal thin film 15, water or the like is absorbed in the interface of them.
The present invention is intended to address the problem of the electrode in the above conventional resistor, and the object of the invention is to provide a resistor improved in reliability, which has low connection resistance and capable of realizing low wiring resistance, and also is improved in adhesive strength between the substrate and the upper electrode layer, between the substrate and the first thin film of side electrode, between the first thin film and the second thin film, and between the second thin film and the first plated film.